This invention is related to difunctionalized oligomers of polyarylene polyethers, and more particularly to the preparation of (a) .alpha.,.omega.-bis(2,6-dimethylphenol)-poly(2,6-dimethyl-1,4-phenylene oxide) ("PPO--2OH" for brevity), and (b) .alpha.,.omega.-bis(2,6-dimethylthiophenol)-poly(2,6-dimethyl-1,4-phenylen e sulfide) ("PPS--2SH") for brevity), by the oxidative copolymerization of 2,6-dimethylphenol (DMP) with 2,2'-di-(4-hydroxy-3,5-dimethylphenyl)propane ("TMBPA"), and of 2,6-dimethylthiophenol (DMTP) with 2,2'-di(4-thiol-3,5 dimethylthiophenyl)propane ("TMBTPA").
Because of poly(phenylene sulfide) (PPS) oligomers are presently less desirable than the poly(phenylene oxide) (PPO) oligomers, both from the viewpoint of physical and chemical properties as well as economics of manufacture, this specification is particularly devoted to the preparation of the latter PPO oligomers, it being understood that analogous procedures may be used to prepare the corresponding PPS oligomers.
Though various PPO--2OH and PPS--2SH oligomers may be difunctionalized as disclosed in my copending application Ser. No. 586,678 the disclosure of which is incorporated by reference thereto as if fully set forth herein, the best embodiment of the difunctionalized PPO-2OH is provided by oligomers of narrowly defined molecular weight which was not heretofore appreciated. Nor could such oligomers be tailored by any known process.
It will be appreciated that despite the essentiality of making perfectly bifunctional PPO--2OH having the desired mol wt, it has only recently been possible to convert the terminal OH groups to vinyl functional groups by phase transfer catalyzed (PTC) reactions, as described in my parent application, inter alia. Under two-phase, namely, aqueous NaOH-organic solvent PTC reaction conditions, the nucleophilicity of a phenol does not depend only on its chemical structure but also on its onium phenolate lipophilicity. A higher lipophilicity of the onium phenolate leads to better and faster extraction into the organic phase. This happens to be a fortuitous situation in which the nucleophilicity of a phenol present at the chain ends of a polymer is fortunately higher than that of its low mol wt homolog. This circumstance permits achieving, for the first time, essentially quantitative PTC polyetherifications of a polymer with phenol chain ends. Though the chain ends can provide either ethers or esters, the greater stability, under acidic or basic hydrolytic conditions, of the ethers make the ether bonds more desirable than the ester bonds.
It is known that 2,6-disubstituted phenols cannot be etherified to high conversions under normal Williamson reaction conditions, but can be quantitatively etherified in the presence of phase transfer catalsysts, as disclosed by McKillop, A., Fiaud, J. C., and Hug, R. P., Tetrahedron 30, 1379 (1974). Under PTC conditions I have quantitatively etherified the 2,6-dimethylphenol chain end of poly(2,6-dimethyl-1,4-phenylene oxide) ("PPO--OH") as disclosed in my copending U.S. patent application Ser. No. 586,679 filed Mar. 6, 1984. When the etherification was performed with an .alpha.,.omega.-di(electrophilic) oligomer it leads to an ABA triblock copolymer containing PPO as the A segments, as disclosed by Percec, V., and Nava, H., Makromol. Chem. Rapid Commun., 5, 319 (1984).
Thus, I chose .alpha.,.omega.-bis(2,6-dimethylphenol)-poly(2,6-dimethyl-1,4-phenylene oxide) ("PPO-2OH") as the oligomer both for the synthesis of block copolymers as well as for the preparation of .alpha.,.omega.-bis(vinylbenzyl)-poly(2,6-dimethyl-1,4-phenylene oxide) ("PPO--2VB").
PPO may be difunctionalized by esterification as is disclosed in "Reactions of Poly(phenylene Oxide)s with Quinones. I. The Quinone-Coupling Reaction Between Low Molecular Weight Poly(2,6-Dimethyl-1,4-phenylene oxide) and 3,3',5,5'-tetramethyl-4,4'-Diphenoquinone", by Dwain M. White, Jour. of Polym. Sci., Polym. Chem. Ed., Vol 19, 1367-1383 (1981). Using a stoichiometric ratio of PPO-OH having a narrowly defined mol wt, and, 3,3',5,5'-tetramethyl-4,4'-diphenoquinone produces PPO--2OH chains having mol wts in a range not well-suited for difunctionalization.
Another method for preparing PPO--2OH is based on the condensation of two PP--OH via their phenyl end groups using formaldehyde and a Lewis acid, using a stoichiometric ratio of PPO--OH and formaldehyde. Still another method is based on the oxidative copolymerization of 2,6-dimethylphenol (DMP) and 2,2'-di(4-hydroxy-3,5-diemthylphenyl)propane (or, tetramethyl bisphenol-A, TMBPA). The oxidation potential of the TMBPA is lower than that of DMP, and therefore, for a low ratio between DMP and TMBPA and specified reaction conditions and time, "prefectly" bifunctional PPO--2OH with mol wt in the range from 500-600 can be obtained. Since the reaction is performed in solution, and the mol wt of the polymer is controlled by the ratio between TMBPA and DMP, it is essential to stop the polymerization at the appropriate time. Failure to do so results in a PPO--2OH oligomer with poor functionality and uncontrolled mol wt. See Heitz, W., Stix, W., Kress, H. J., Koch, W. and Risse, W., Polym. Prepr., 25(1), 136 (1984); and, Risse, W. and Heitz, W., Makromolekulares Kolloquim, Freiburg FRG, Preprints, p 50 (1985). By "prefectly" I specify that no oligomer having a functionality other than 2 can be detected.
Other difunctionalized PPO oligomers are disclosed in U.S. Pat. No. 3,663,625 to Neville, R. G. None of the prior art syntheses was concerned with reaction of alkali metal salts ("bisphenolates") of an oligomer of PPO or PPS which had been tailored to have phenol chain ends which could then be converted to vinyl functional groups. Nor was the importance of having perfectly bifunctional PPO or PPS recognized, at least in so far as its subsequent conversion to ether or ester chain ends having vinyl functionality.
The problem was to advance the concept of a phase transfer catalyzed etherification of a PPO oligomer having a single phenol chain end to an oligomer with two phenol chain ends. The preparation of comb-like polymers from the monofunctionalized oligomers is disclosed in my copending U.S. patent application Ser. No. 586,679 filed Mar. 6, 1984, and in an article titled "Comb-Like Polymers and Graft Copolymers from Macromers" 2. Synthesis, Characterization and Homopolymerization of a Styrene Macromer of Poly(2,6-Dimethyl-1,4-Phenylene Oxide)" by Percec, V., Rinaldi, P. and Auman, B. Polymer Bulletin 10, 397-403 (1983), the disclosures of which are incorporated by reference thereto as if fully set forth herein.
This invention offers an elegant and convenient solution to that problem.